1. Field of the Invention
The present invention relates to removing sulfur species from a hydrocarbon stream, and is specifically directed to a method of removing sulfur components selected from the group consisting of mercaptans, organic sulfides and disulfides from a hydrocarbon stream in the absence of extraneously added hydrogen.
More specifically, the present invention is directed to a process for adsorbing sulfur species, i.e., disulfides, organic sulfides and mercaptans, from an olefinic hydrocarbon stream, e.g., containing propylene and propane, by contacting the hydrocarbon stream with a catalyst capable of adsorbing the sulfur species, i.e., one which preferably contains metal oxides selected from the group consisting of a mixture of cobalt and molybdenum oxides, a mixture of nickel and molybdenum oxides, or nickel oxide, in the absence of extraneously added hydrogen and under conditions suitable for adsorbing the sulfur species from the hydrocarbon stream, i.e., a temperature within the range of about 75.degree. C.-175.degree. C., but preferably about 75.degree. C.; a pressure within the range of 150 psig-1100 psig, but preferably about 175 psig; and a liquid hourly space velocity within the range of about 0.5 v/v/h-10 v/v/h, but preferably about 1 v/v/h to form a resultant hydrocarbon stream containing a reduced amount of the sulfur species, i.e. less than about 20% by weight, relative to the initial content of the sulfur species in the hydrocarbon feedstream.
2. Discussion of Background and Material Information
In the petroleum industry, higher olefin plants typically use a propylene feedstock containing various amounts of propylene, propane, butylenes and butanes, and commonly a mixture of 50% propylene and 50% propane. The typical propylene feedstock normally contains from about 5-50 ppm of various sulfur species. Dimethyl sulfides, methyl ethylsulfides, diethyl sulfides, dimethyl disulfide, methyl mercaptan and ethylmercaptan are the most typical of the sulfur species present in these feedstreams.
During oligomerization, however, the sulfur species tend to become incorporated in the higher olefins. Although higher olefins containing sulfur can be used as feedstock for various chemical processes, the sulfur in the higher olefin hydrocarbon streams typically contribute to the production of resultant product streams which are lower in quality than if sulfur were not present in, or removed from, the olefinic hydrocarbon feedstream.
Prior to the present invention, attempts have been to desulfurize higher olefin products over a sacrificial nickel catalyst; however, such processes also suffer from numerous disadvantages.
A typical example of a known desulfurizing technique which has been proposed for this purpose involves subjecting dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) to a sulfided conventional hydrodesulfurization catalyst, such as cobalt-molybdenum (CoMo) or nickel-molybdenum (NiMo) on alumina. In such a catalyst sulfiding, inactive metal oxides are converted to metal sulfides as described hereinafter. A stream of naphtha or gas oil containing 6,000-20,000 wppm DMS or DMDS is mixed with a stream of hydrogen gas and heated to a temperature within the range of 200.degree. C. to 300.degree. C. As the mixture is passed over the catalyst, in its metal oxide form, the sulfur species are thermally and catalytically decomposed by the hydrogen to produce hydrogen sulfide and methane as follows: CH.sub.3 -S-CH.sub.3 +H.sub.2 &gt;2CH.sub.4 +H.sub.2 S; hydrogen sulfide reacts with metal oxides in the catalyst to form the corresponding sulfides: EQU CoO+H.sub.2 S.fwdarw.CoS+H.sub.2 O; EQU 3NiO+2H.sub.2 S+H.sub.2 .fwdarw.Ni.sub.3 S.sub.2 +3H.sub.2 O; and EQU MoO.sub.3 +2H.sub.2 S+H.sub.2 .fwdarw.MoS.sub.2 +3H.sub.2 O.
These metal sulfide catalysts are conventionally used with hydrogen to catalytically convert sulfur in hydrocarbon feedstocks to hydrogen sulfide, thus allowing the sulfur to be removed by simple stripping.
A similar process using hydrogen cannot be used to hydrodesulfurize propylene as these catalysts are well known to catalyze hydrogenation of alkenes. Although not wishing to be bound to any particular theory, it is believed that hydrodesulfurization, using metal sulfide catalysts, would hydrogenate propylene to undesirable propane in combination with or even preferentially over, sulfur removal.
U.S. Pat. No. 2,959,538, WEIKART et al., is directed to a process for hydrodesulfurizing petroleum oil feed containing naphtha, kerosene, and diesel oil fractions which involves passing hydrofined products through a zinc oxide drum which is at a pressure of 200 psig so as to convert the hydrogen sulfide present as a result of the hydrofining to H.sub.2 O and zinc sulfide before passing the desulfurized hydrocarbon and hydrogen vapors and gases to a fractionator.
U.S. Pat. No. 3,063,936, PEARCE, relates to desulfurization of hydrocarbon oils, which are intended to be used for the manufacture of methanol from a mixture of carbon monoxide and hydrogen produced by steam reforming of a straight-run naphtha. The desulfurization occurs in three stages including one wherein vaporized hydrocarbon oil is passed over a contact material comprising zinc oxide, manganese oxide or iron oxide, but preferably zinc oxide, at a temperature between about 350.degree. C. and 450.degree. C., and at a pressure between about 1 and 50 atmospheres, prior to passing the vaporized hydrocarbon, together with hydrogen, at a temperature between 350.degree. C. and 450.degree. C., and at a pressure between about 1 and 50 atmospheres, over a hydrodesulfurization catalyst, followed by contacting the resultant product with a hydrogen sulfide absorbing catalyst. It is disclosed that the contact material comprises zinc oxide, manganese oxide or iron oxide, with zinc oxide being preferred. The hydrodesulfurization catalysts are disclosed as being selected from the group of palladium, platinum or cobalt molybdate, supported on alumina wherein the cobalt molybdate are composed of oxides of cobalt and molybdenum. It is disclosed that any suitable material which is capable of absorbing hydrogen sulfide may be used in the third stage of the process but that absorbing material preferably includes zinc oxide, manganese oxide or iron oxide with zinc oxide is preferred.
U.S. Pat. No. 3,660,276, LACEY, is directed to a process for desulfurizing hydrocarbon distillate oils wherein a mixture of the oil vapor in the carbon dioxide-containing hydrogenating gas is passed over a hydrodesulfurization catalyst and then over a material capable of absorbing hydrogen sulfide and eliminating any carbonyl sulfide present either by absorbing the carbonyl sulfide or by converting it to hydrogen sulfide and absorbing the hydrogen sulfide. It is disclosed that the hydrodesulfurization catalyst may contain molybdenum or nickel or cobalt with a preferred catalyst containing molybdenum which is promoted by the presence of nickel and supported on alumina. Another disclosed example of hydrodesulfurization catalysts is molybdenum coated with cobalt and supported on alumina. Materials which are disclosed as being capable of quantitatively absorbing hydrogen sulfide and also eliminating carbonyl sulfides is zinc oxide, with zinc oxide-copper oxide compositions being disclosed as an alternative.
U.S. Pat. No. 4,088,736, COURTY, is directed to a process for purifying a hydrogen sulfide-containing gas which involves absorbing the hydrogen sulfide onto a mass composed of zinc oxide, alumina, and a Group IIA metal oxide, wherein a large proportion of the Group IIA metal oxide is in the form of aluminate or silicoaluminate. The solid contact materials disclosed as being useful for this purpose are described as being thermally stable and regenerable and contain, by weight, 20-85% of zinc oxide, 0.9-50% of alumina, and 2-45% of oxide of a Group IIA metal with or without additional elements which may be 0.1-30% by weight silica, or one or several oxides of a metal selected from the group consisting of copper, cadmium, titanium, zirconium, vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, and nickel wherein the latter oxides are disclosed as making the absorption of H.sub.2 S, COS, CS.sub.2 and the regeneration of the absorption material easier.
U.S. Pat. No. 4,300,999, relates to gas oil purification wherein hydrogen sulfide is absorbed by passing partially vaporized oil, hydrogen-containing gas and hydrogen over zinc oxide, wherein the organic sulfur compounds which are removed are disclosed as being carbonyl sulfides (COS) and carbon disulfide (CS.sub.2).
U.S. Pat. No. 4,313,820, FARHA, is directed to the removal of hydrogen sulfide from a fluid stream by contacting the fluid stream which contains hydrogen sulfide with an absorbing composition which is composed of zinc, titanium and at least one promoter selected from the group consisting of vanadium, chromium, manganese, iron, cobalt, nickel, molybdenum, rhenium, and compounds thereof. It is disclosed that if organic sulfur compounds are present in the fluid stream, the absorbing composition acts as a hydrodesulfurization catalyst to convert the sulfur in the organic sulfur compounds to hydrogen sulfide which is subsequently removed from the fluid stream by the absorbing composition. If olefin contaminants are present in the fluid stream, the absorbing composition acts as a hydrogenation catalyst to hydrogenate the olefin contaminants to paraffins.
U.S. Pat. No. 4,533,529, LEE, is directed to the removal of sulfur species from a Claus plant tail gas stream by contacting with zinc oxide in the presence of sufficient reducing equivalents for conversion of sulfur compounds to hydrogen sulfide; alternatively, the sulfur compounds are converted to hydrogen sulfide prior to contacting with the zinc oxide.
U.S. Pat. No. 4,571,445, SLAUGH, is directed to reducing the level of sulfur compounds from liquid conjugated diolefin hydrocarbons by contacting the sulfur compound-bearing hydrocarbon liquids with sorbents prepared by combining particulate alumina with at least one compound decomposable to sodium oxide, barium oxide, calcium oxide, or a salt decomposable to potassium oxide.
U.S. Pat. No. 4,593,148, JOHNSON, is directed to the removal of hydrogen sulfide from gaseous streams by contacting the gas streams with a sorbent material which is composed of copper oxide and zinc .oxide, preferably wherein the absorbent material is prepared by coprecipitating hydroxides of copper and zinc, and subsequently heating the hydroxides so as to convert the hydroxides to CuO ZnO with aluminum oxide being disclosed as being an optional component of the sorbent material.
GB 1,142,339, BADISCHE ANILIN & SODA-FABRIK AKTIENGESELLSCHAFT, is directed to the removal of carbonyl sulfide from gas mixtures using metal oxides.